<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>包装类型</title>
</head>

<body>
  <script>

    // ============================== 包装类型 ==============================
    const str = 'andy'
    console.log(str.length)
    console.log(str.substring(1))
    
    // 包装过程
    const res = new String('andy')
    

  </script>
</body>

</html>